encoding: add an encoding.leb128 module with tests (#17880)

vlib/encoding/leb128/leb128.v

@@ -0,0 +1,129 @@
+module leb128
+
+// encode_i32 encodes the `value` as leb128 encoded byte array
+pub fn encode_i32(value i32) []u8 {
+	mut result := []u8{cap: 4}
+	mut val := value
+	mut i := 0
+	for {
+		mut b := u8(val & 0x7f)
+		val >>= 7
+		if (val == 0 && b & 0x40 == 0) || (val == -1 && b & 0x40 != 0) {
+			result << b
+			break
+		}
+		result << b | 0x80
+		i++
+	}
+	return result
+}
+
+// encode_i64 encodes the `value` as leb128 encoded byte array
+pub fn encode_i64(value i64) []u8 {
+	mut result := []u8{cap: 8}
+	mut val := value
+	for {
+		mut b := u8(val & 0x7f)
+		val >>= 7
+		if (val == 0 && b & 0x40 == 0) || (val == -1 && b & 0x40 != 0) {
+			result << b
+			break
+		}
+		result << b | 0x80
+	}
+	return result
+}
+
+// encode_u64 encodes the `value` as leb128 encoded byte array
+pub fn encode_u64(value u64) []u8 {
+	mut result := []u8{cap: 8}
+	mut val := value
+	for {
+		mut b := u8(val & 0x7f)
+		val >>= 7
+		if val == 0 {
+			result << b
+			break
+		}
+		result << b | 0x80
+	}
+	return result
+}
+
+// encode_u32 encodes the `value` as leb128 encoded byte array
+pub fn encode_u32(value u32) []u8 {
+	mut result := []u8{cap: 4}
+	mut val := value
+	for {
+		mut b := u8(val & 0x7f)
+		val >>= 7
+		if val == 0 {
+			result << b
+			break
+		}
+		result << b | 0x80
+	}
+	return result
+}
+
+// decode_i32 decodes an i32 from the given leb128 encoded array `value`
+pub fn decode_i32(value []u8) i32 {
+	mut result := int(0)
+	mut shift := 0
+	for b in value {
+		result |= b & 0x7f << shift
+		shift += 7
+		if b & 0x80 == 0 {
+			if shift < 32 && b & 0x40 != 0 {
+				result |= ~0 << shift
+			}
+			break
+		}
+	}
+	return result
+}
+
+// decode_i64 decodes an i64 from the given leb128 encoded array `value`
+pub fn decode_i64(value []u8) i64 {
+	mut result := u64(0)
+	mut shift := 0
+	for b in value {
+		result |= u64(b & 0x7f) << shift
+		shift += 7
+		if b & 0x80 == 0 {
+			if shift < 64 && b & 0x40 != 0 {
+				result |= ~u64(0) << shift
+			}
+			break
+		}
+	}
+	return i64(result)
+}
+
+// decode_u64 decodes an u64 from the given leb128 encoded array `value`
+pub fn decode_u64(value []u8) u64 {
+	mut result := u64(0)
+	mut shift := 0
+	for b in value {
+		result |= u64(b & 0x7f) << shift
+		if b & 0x80 == 0 {
+			break
+		}
+		shift += 7
+	}
+	return result
+}
+
+// decode_u32 decodes an u32 from the given leb128 encoded array `value`
+pub fn decode_u32(value []u8) u32 {
+	mut result := u32(0)
+	mut shift := 0
+	for b in value {
+		result |= u32(b & 0x7f) << shift
+		if b & 0x80 == 0 {
+			break
+		}
+		shift += 7
+	}
+	return result
+}